1. Field
The field hereof is container covers. More particularly, the present disclosure relates to an improved method of making a flexible container cover with an elastic encircle opening.
2. Prior Art
There are number of different types of container or plate covering systems of which I am aware.
One type is a fixed-size container lid which is sized and manufactured to fit a specific container. For example plastic food storage containers such as those sold under the trademark Tupperware generally have matching plastic lids. This approach requires that a specific matching lid be available to cover the container. The lids cannot be used on a different size or shape container.
The second type of product offering and system for covering plates and bowls as well as containers is flexible plastic film and aluminum foil generally provided in a continuous sheet on a roll, such as rolls of plastic wrap sold under the trademark Saran or foil sold under the trademark Reynolds. In order to cover a plate or bowl, the user simply cuts a length of the film or foil and manually molds the cut film or foil over the container. Although this system is flexible enough to cover containers of various sizes and shapes, it is often difficult to cut the film to the correct length and apply it to a container without the film sticking to itself or its edges lifting from the container. Additionally it is difficult to re-cover a container with the same piece of film since plastic films lose their ability to stick to the container after prolonged use, and aluminum foils tear and become wrinkled. Also, foil is not transparent and thus does not allow users to see what is stored in the container. And because it is metallic it cannot be used in some microwave ovens.
The third type of bowl, plate, and container cover is a flexible film cover with an elastic band sewn or stitched around the opening. This type of product has been commercially available and for many years. The same or a similar product is also sold as a shower cap. SC Johnson Co. has sold this type of container cover under their trademark Quick Covers. This type of cover is made from a circular sheet of plastic film, also known as a blank, with a strip of elastic sewn around the perimeter. The elastic, being shorter than the circumference of the blank, gathers the edge of the blank to the center and creates a cover similar in appearance to a shower cap.
There are three drawbacks to this design. The first is that it is unsanitary and unsightly for use with food items due to the fact that the elastic band is stitched to the plastic so that the thread and the ends of the elastic are not contained within, and often hang from the cover. The elastic is also prone to separating at the stitches after a number of uses. The second drawback is that these covers cannot be mass produced on high speed machinery because the elastic must be sewn around the perimeter of the sheet. The third drawback is that these covers do not fit both elliptical and rectangular containers with similar size openings, nor do they fit elongated rectangular shaped container, and therefore have relatively low versatility.
U.S. Pat. Nos. 2,490,451 to Magid (1949) and 3,035,960 to Farkas et al. (1962) disclose covers with an elastic band heat sealed into a hem along the periphery of a circular sheet of plastic film. Although these covers eliminate the unsanitary and undesirable aesthetics of the above stitched type of cover, they do not fit both elliptical and square containers with similar size openings, nor do they fit elongated rectangular containers. Furthermore, the method of manufacturing the covers of both patents requires multiple forming head to form the sheet and the band. Also it is difficult to remove the finished covers from the sealing apparatus, and thus they cannot be made on high speed machinery. Finally, these covers completely enclose the elastic band in a sealed edge which is not functional in a microwave oven because the air trapped within the hermetically sealed hem will expand when heated in a microwave, which can cause the hem to burst, thereby destroying the cover.
In my above copending application Ser. No. 11/840,019 I disclose an improved more versatile cover and method of manufacture. This cover is made from a rectangular sheet of plastic film material, or blank, and an elastic band. The sheet has a predetermined amount of material cut from each corner. The sheet is placed onto a table between four posts that extend from the table. The sheet is positioned so that a post lines up with each corner of the sheet. A rubber band is stretched across the four posts into a similar shaped rectangle and rests just above the sheet. The stretched rubber band now has four sides which correspond to the four sides of the sheet. The side edges of the sheet are folded inward and over the stretched band and heat sealed directly to the sheet, sealing the band within four pockets that are formed along the sides of the sheet. Each corner of the stretched band is released from its post, allowing the band to relax and pull the four corners of the sheet toward the center to form the cover.
While this cover and its method of manufacture is a substantial improvement over prior covers, there are three areas that could be improved further. The first area in need of improvement is that the forming method requires a cut in each corner to allow room for the elastic band holding post, which leaves an opening in the hem at each corner of the cover exposing a portion of the band. While this eliminates the problem discussed above of a bursting hem when used in a microwave, and does not cause a functional problem because the location of the cut or hole is below the rim of the container being covered, the exposed band has the potential to look like a manufacturing defect to some customers. The second area in need of improvement is the process step of stretching and placing the rubber band around the holding posts. This step requires a high degree of precision to position the stretched rubber band directly above the sheet so that the sides of the sheet can be folded over the band in order to be heat sealed. This step slows the manufacturing process and limits the process capability for high speed automation. There is also a limitation in my above referenced applications in that the cover formed by the folding over an elastic band method requires that the starting blank have substantially straight sides. While a rectangular blank provides maximum flexibility in being able to cover round, rectangular, square, oval, or any other shaped container, there could be a situation where a customer would want a cover made from a round blank.